Trends of the environmental spread of mcr genes in Latin America
Authors: João Pedro Rueda Furlan, Fábio P Sellera, Eliana Guedes Stehling
Journal: The Lancet Microbe (2023)

The rapid spread of mobile colistin resistance (mcr) genes in Enterobacterales, recovered mainly from humans and food-producing animals, represents the breach of the last-resort antimicrobials used against multidrug-resistant Gram-negative bacteria.1El-Sayed Ahmed MAE Zhong LL Shen C Yang Y Doi Y Tian GB Colistin and its role in the era of antibiotic resistance: an extended review (2000–2019).Emerg Microbes Infect. 2020; 9: 868-885Crossref PubMed Scopus (0) Google Scholar Calero-Cáceres and Balcázar2Calero-Cáceres W Balcázar JL Evolution and dissemination of mobile colistin resistance genes: limitations and challenges in Latin American countries.Lancet Microbe. 2023; (published online June 2.)https://doi.org/10.1016/S2666-5247(23)00152-0Summary Full Text Full Text PDF PubMed Google Scholar previously suggested that there are potential gaps in the literature on the evolution and dissemination of mcr variants in Latin American countries. We present the little known aspects of the environmental spread of mcr genes in these countries. In Latin America, Argentina, Bolivia, and Brazil have the highest number of mcr-positive strains of Enterobacterales, which were widely reported in samples associated with humans and animals.3Mendes Oliveira VR Paiva MC Lima WG Plasmid-mediated colistin resistance in Latin America and Caribbean: a systematic review.Travel Med Infect Dis. 2019; 31101459Crossref PubMed Scopus (23) Google Scholar Conversely, the prevalence of mcr genes in the environment is underestimated. Despite mcr genes (mcr-1 to mcr-9) being reported in environmental samples (eg, in water, soil, and sediment) collected during 2015–20 from Brazil, Colombia, and Ecuador, studies of mcr genes are concentrated in Brazil. The mcr genes derived from the environment in Brazil, Colombia, and Ecuador were described in Escherichia coli and uncultured microorganisms from environmental samples of urban, rural, and coastal areas. However, only the plasmid-mediated mcr-1 gene has been housed in environmental E coli strains, highlighting the international high-risk clones ST10 and ST131 (appendix p 2). IncX4 and IncI2 plasmids are key vectors that spread the mcr-1 gene in the environment. In Brazil and Ecuador, environmental E coli strains that are positive for mcr-1 also carried extended-spectrum β-lactamase-encoding genes. Worryingly, mcr genes were reported in drinking and irrigation waters, evidencing the environmental transmission of colistin resistance (appendix p 2). In 2021, irrigation water was associated with the contamination of vegetables by E coli carrying mcr-1.4Díaz-Gavidia C Barría C Rivas L et al.Isolation of ciprofloxacin and ceftazidime-resistant enterobacterales from vegetables and river water is strongly associated with the season and the sample type.Front Microbiol. 2021; 12604567Crossref PubMed Scopus (6) Google Scholar In China and Europe, the decrease in mcr prevalence could be related to the banning of colistin-positive additives for animals.5Olaitan AO Dandachi I Baron SA Daoud Z Morand S Rolain JM Banning colistin in feed additives: a small step in the right direction.Lancet Infect Dis. 2021; 21: 29-30Summary Full Text Full Text PDF PubMed Google Scholar In Latin America, only Argentina and Brazil have done so; other countries continue to acquire polymyxin derivatives, mainly for veterinary purposes.2Calero-Cáceres W Balcázar JL Evolution and dissemination of mobile colistin resistance genes: limitations and challenges in Latin American countries.Lancet Microbe. 2023; (published online June 2.)https://doi.org/10.1016/S2666-5247(23)00152-0Summary Full Text Full Text PDF PubMed Google Scholar, 5Olaitan AO Dandachi I Baron SA Daoud Z Morand S Rolain JM Banning colistin in feed additives: a small step in the right direction.Lancet Infect Dis. 2021; 21: 29-30Summary Full Text Full Text PDF PubMed Google Scholar In Brazil, there appears to be a decrease of mcr genes in the environment. Notably, animal effluents exert selective pressure on the environment, selecting the mcr genes and facilitating the transmission to humans via waterborne and foodborne routes. Although environmental bacteria are possible progenitors of mcr genes,6Mmatli M Mbelle NM Osei Sekyere J Global epidemiology, genetic environment, risk factors, and therapeutic prospects of mcr genes: a current and emerging update.Front Cell Infect Microbiol. 2022; 12941358Crossref PubMed Scopus (6) Google Scholar they only seem to be of interest when they enter clinical settings. In addition to factors that can influence the selection of mcr genes,2Calero-Cáceres W Balcázar JL Evolution and dissemination of mobile colistin resistance genes: limitations and challenges in Latin American countries.Lancet Microbe. 2023; (published online June 2.)https://doi.org/10.1016/S2666-5247(23)00152-0Summary Full Text Full Text PDF PubMed Google Scholar, 7Umair M Hassan B Farzana R et al.International manufacturing and trade in colistin, its implications in colistin resistance and One Health global policies: a microbiological, economic, and anthropological study.Lancet Microbe. 2023; 4: e264-e276Summary Full Text Full Text PDF PubMed Google Scholar climate change can have indirect effects on colistin resistance through complex ecological and environmental pathways.8Hernando-Amado S Coque TM Baquero F Martínez JL Defining and combating antibiotic resistance from One Health and Global Health perspectives.Nat Microbiol. 2019; 4: 1432-1442Crossref PubMed Scopus (412) Google Scholar Globalisation has increased the long-distance dispersal mechanisms of colistin resistance in a borderless world. Therefore, this issue should be addressed as a global health problem that requires public health authorities to pay greater attention to the environmental factors. We declare no competing interests. Download .pdf (.29 MB) Help with pdf files Supplementary appendix